In a process termed emmetropization, the growth of eye length is regulated by visual experience to match the eye's optics and to compensate for genetic variation in corneal/lens curvature and power. High acuity photopic vision and, thus, the signals that guide emmetropization are initiated by light absorption photopigments found in the long wavelength (L) and middle-wavelength (M) sensitive cone photoreceptors. Changes in the pattern of light and dark in the retinal image that characterize blurred versus sharply focused images are monitored by a biological process to stop eye growth when the correct length for coordinated plano (neutral) optics is reached. However, in myopic individuals, the relative axial length of the eye to overall eye size continues to increase during development, past a length that provides near-optimal focusing of distant objects, leading to increasingly pronounced myopia.
The rate of incidence of myopia is increasing at alarming rates in many regions of the world. Until recently excessive reading during childhood was believed to be the only identifiable environmental or behavioral factor linked to the occurrence of myopia, although genetic factors were suspected. Limiting reading (and encouraging more outdoor activity) are presently the only practical techniques for preventing excessive eye lengthening in children, and corrective lenses, including glasses and contact lenses, represent the primary means for ameliorating eye-length related disorders, including myopia. While these measures optically correct the refractive errors associated with eye-length related disorders they do not address the underlying cause which is excessive growth of eye length.
Thus, there remains a need for methods of detecting a susceptibility to an eye-length related disorder, and treatments for such individuals that would prevent excessive eye lengthening.